The embodiments described herein relate generally to imaging apparatuses, and more specifically, to an apparatus including at least one of an X-ray source and X-ray detector mounted to a rotational arm.
In a number of clinical applications, imaging apparatus, and more particularly X-ray apparatuses, which include an X-ray source and X-ray detector mounted to a rotational arm are common These systems provide the ability to rotate the X-ray source and detector to varying angles to obtain images without requiring the patient to move. A mammography system, for example, typically comprises an X-ray source, an X-ray detector, a breast support plate, and a breast compression plate. The source and detector are mounted to opposing ends of an arm, such as a C-arm, and the arm is disposed to rotate around the breast support and compression plates. The breast is positioned between the breast support and breast compression plates to hold the breast in place during mammography, and is arranged between the source and the detector on the opposing ends of the C-arm. During mammography, the C-arm is rotated about the breast plates such that images of the breasts are acquired from varying angles.
For construction reasons, and due to the varying weights of the components, the center of mass of the rotatable C-arm is typically spaced apart from the axis of rotation, and is therefore “unbalanced” about the axis of lateral rotation. In an unbalanced system, a significant torque must be applied to rotate the arm to a desired position. It is desirable, however, to reduce the amount of force required to rotate the arm, to simplify use of the equipment for medical personnel.
Current systems used to reduce the amount of force required to rotate the arm include counterbalance mechanisms. These counterbalance mechanisms used in mammography systems balance the gravitational torque of the rotating arm only partially, leading to much higher power requirement of the actuation system (motor, gear, etc.).
One example of an apparatus and method used to balance the system includes counterweights. The counterweights provide a counteractive torsional force. While counterweights significantly reduce the torsional force that must be applied when rotating the arm, they add significantly to both the weight and cost of the system. Furthermore, the counterweights make it very difficult to move the mammography system from place to place when desired.
Another example of an apparatus and method used to balance the system includes the use of a gas spring. The gas spring is used to counterbalance the arm through a gear set. Such a mechanism may only partially balance the arm. It is estimated that 90% of the motor power of the system is used to compensate for the unbalanced gravitational load. In addition, it is estimated that the gas spring force can degrade up to 20% over its lifespan and has very limited cycle life. Accordingly, the use of a gas spring limits the fatigue life of the system and increases the need for service.
As a result, it is desirable to provide alternate systems and methods for balancing a mammography or other imaging systems comprising an arm in which the torsional force required for rotation is reduced.